The present invention relates to a memory circuit, and more particularly to a memory circuit which can assume a predetermined memory state when the application of power is initiated by a power switch.
In a data processor such as an electronic computer or a microcomputer, a large number of memory devices are used, and among these memory devices some must be set to a predetermined memory state such as a reset state prior to the operation of the data processor. To that end, bistable memory circuits which can be automatically reset upon the switching on of a power supply have been used in large numbers. These memory circuits are generally called power-on-reset type memory circuits. In such a power-on-reset type memory circuit, a flip-flop circuit is used as a memory section and a difference is produced between the potential rises at a pair of cross-connection points in the flip-flop circuit which are caused by a power supply voltage upon switching on the power supply. This is done by making the electrical characteristics of a pair of load circuits in the flip-flop circuit unbalanced, to thereby automatically and simultaneously set the cross-connection point connected to the load circuit having the larger current feed capability at logic "1" and the cross-connection point connected to the load circuit having the smaller current feed capability at logic "0". Thus, the above-mentioned reset operation can be achieved.
However, in the event that the known power-on-reset type memory circuit
is in the set state when the power supply is switched off and after a relatively short period of time is again switched on, the memory circuit cannot be automatically set to the reset state. Consequently, an information processor making use of such memory devices had a shortcoming that a malfunction would be caused thereby. More particularly, that one of the pair of cross-connection points in the flip-flop which is held at the power supply level in the set state would not immediately be brought to the ground level even if the power supply were switched off, but would be discharged gradually towards the ground level. Accordingly, if the power supply were switched on during this discharging process, then the flip-flop would not assume the reset state but would be set to the set state.
As described above, the power-on-reset type memory device of the prior art had a in that if the time interval between the switching-off and switching-on of the power supply were short, the power-on-reset function could not operate reliably.